1. Field of the Invention
The present invention relates to an integrated circuit (IC) such as a semiconductor memory and, more specifically, to a chip address storing section of an integrated circuit for selecting a semiconductor chip when an address assigned in advance to the chip coincides with a chip address supplied from outside the chip.
2. Description of the Related Art
A conventional data processing system, such as a microcomputer using a plurality of semiconductor memories, has the circuit arrangement as shown in FIG. 7 or 8 in order to select one of a plurality of memory chips.
The microcomputer system shown in FIG. 7 includes, for example, 4-bit input/output (I/O) buses 70 serving as both a data bus and an address bus, a plurality of memory chips 711 to 715 each having 4-bit I/O terminals, control input terminals supplied with a reading control read enable signal RE, a writing control write enable signal WE, and register selecting address signals RA0 to RA2, and a chip selection terminal supplied with a corresponding one of chip selecting chip enable signals CE1 to CE5 and chip selecting signal lines 701 to 705 through which the chip enable signals CE1 to CE5 are supplied to the respective memory chips 711 to 715.
The microcomputer system shown in FIG. 8 differs from that shown in FIG. 7 in that memory chips 811 to 815 each have three chip address setting terminals S0 to S2 externally supplied with (power supply or ground) potentials for assigning, e.g., 3-bit chip addresses, and the chip selection terminals thereof are supplied with the same chip enable signal CE. The memory chips 811 to 815 are selected when the addresses assigned to the chips by combination of the potentials supplied to the chip address setting terminals S0 to S2, coincide with chip addresses supplied from outside the chips.
However, the microcomputer system shown in FIG. 7 requires the chip selecting signal lines 701 to 705 the number of which is equal to that of the memory chips. The more the memory chips, the larger the occupied area of the memory chips mounted on a printed circuit board in the microcomputer system. In the system shown in FIG. 8, the memory chips 811 to 815 need the plural chip address setting terminals S0 to S2, the number of pads on each chip increases, as does the area of the chip, thus increasing in chip cost.
As described above, the conventional microcomputer system requires a plurality of chip selecting signal lines the number of which is equal to that of chips or a plurality of chip address setting terminals for assigning chip addresses to semiconductor chips. Thus, it has a problem in which the area of chips occupied in the system increases and so does the cost of the chips.